Crayon



Patented Sept. 24, 1940 CRAYON Charles E. Daniel, Sandusky, Ohio, assignor to The American Crayon Company, Sandusky,

Ohio, a corporation No Drawing. Application April 18, 1938, Serial No. 202,686

4 Claims.

This invention relates tocrayons of the type which can be applied to a surface and erased therefrom by a dry eraser without leaving a permanent mark. Such crayons find their widest application in school use although other purposes are included. The specific invention to which this application relates is a black crayon intended for use on a light colored surface, and is particularly planned for cooperation with the surface characteristics of a sheet of appropriately-treated glass or other vitreous material, although not limited thereto.

The problems involved in making a dark mark upon a light background are somewhat different from those involved in writing with chalk, soapstone or similar crayon of white or light tints upon dark surfaces, largely because it is more diflicult to erase black or other dark marks without smudging.

Although no extensive research has been conducted in the matter, the difficulties which must be surmounted may be generally stated as being due to the necessity of reconciling several conflicting characteristics, such as the following:

(1) The crayon must be sufficiently tough not to break under bending stresses during writing.

(2) It must be sufficiently hard not to come off on the fingers, and this feature is more important with black or dark colors than with white or light chalks, on account of the greater damage of the dark to clothing, and the like.

(3) It must yield its surface particles to the board readily so as not to demand excessive energy or pressure in writing.

(4) It must not crumble excessively, which crumbling would give dust in writing or cause a blurred mark instead of a sharply defined path of the crayon.

(5) It must be removable by rubbing with a dry eraser and without excessive pressure by such eraser.

(6) When so erased it should be completely removed from the board and not leave any aftertrace, orat least the after trace should be so faint as not to be readily visible.

Although it is obvious that generally speaking any crayon will make a mark on any surface, nevertheless for best results the physical characteristics of the crayon must be properly related to the physical characteristics of the surface on which used.

With the foregoing considerations in mind I have endeavored to produce a crayon which will be smooth-writing, clear, uniform, readily erasable, strong, clean and dustless, and particularly intended for use upon a surface having the characteristics of a dull-finished glass having a -fine even tooth such as is at present being informity in the product and of best performance in use.

As an example of a suitable carbon, I have obtained satisfactory results with, and therefore 20 prefer, charcoal ground to sufficient fineness to break down the cell structure of the wood from which the charcoal is made, and thus permit uniform distribution of the'charcoal in the mix. The physical characteristics of the Wood appar- 25 ently have some effect on the suitability of the charcoal for the present purpose. I have had excellent results with pure willow charcoal. For body material I find a mixture of ground kaolin and calcium carbonate to be satisfactory, this 30 being substantiallythe body material used in ordinary blackboard chalks either white or tinted. As a binder I prefer a mixture of soap and vegetable adhesive. I prefer a vegetable oil soap, for example a pure olive oil soap of the 35 type used in the textile industry, The adhesive may be gum tragacanth or may be locust bean ground to a putty-like consistency.

Formula 1 below shows a composition which in the light of present experience I consider the 0 most desirable for the purposes in view the parts are taken by weight.

Formula 1 Parts 45 Charcoal Kaolin 50 Calcium carbonate 20 'Greaseless black 20 tSoap 2 50 Gum tragacanth or ground locust bean 5 The foregoing ingredients are well mixed to entire homogeneity of distribution, and to about the consistency of putty, and are then extruded, molded or otherwise formed into crayons of the 55 desired size and shape, usually in the form of sticks similar to those of the conventional school room chalk. The mechanical methods employed in such molding are not material to the present invention, but are those well known in the in dustry.

The foregoing formula may be modified as follows, with satisfactory results.

Formula 2 Parts Charcoal Kaolin 20' Calcium carbonate 12 Greaseless black 12 Soap t 2 Ground locust bean 3 Formula 3 Parts Charcoal Kaolin 50 Calcium carbonate 20 Non-acid soap 2 Vegetable adhesive 5 Instead of mixing all the ingredients in a single batch, the vegetable adhesive, the soap and the charcoal may be thoroughly mixed into an entirely homogeneous pasty mass; and the other materials may also be separately mixed, followed by combining the two mixes in a ball mill, colloid mill, or the like to thoroughly incorporate all the ingredients into a perfectly uniform product. After such final homogenizing the material is then shaped into crayons and dried. as usual.

In compounding the foregoing or equivalent formulas the end sought is to provide a crayon in which the surface is friable in minute flakes or granules, the dimensions of which approximate those of the irregularities which constitute the tooth of ground glass which has a distinctly dull surface, and a substantially even feel, without perceptable roughnesses or distinguishable protuberances, but nevertheless not slick. The action of the crayon consists essentially in depositing upon such surface particles individually about the size of or somewhat smaller than the individual irregularities, depositing a slightly greater quantity of such particles than required to fill the hollows. The persistence of the mark upon the writing surface is more due to a mechanical clinging action than to the sort of adhesion which occurs with a wax crayon. Thus a principal purpose of the invention is to so relate the physical characteristics of the crayon to those of the glass surface as to give the same results both for writing and for erasing as occurs with ordinary school room chalk on a finetoothed slate blackboard.

Other modes of applying the principle of my invention may be employed instead of the one explained, change being made as regards the means and steps herein disclosed, provided those stated by any of the following claims or the equivalent of such stated means be employed.

I therefore particularly point out and distinctly claim as my invention:

1. A black crayon consisting of finely pulverized charcoal, kaolin, calcium carbonate, greaseless black, soap and a gum, thoroughly mixed and pressed to shape.

2. A crayon composed of the following ingredients in the following proportions:

Parts Pulverized charcoal 130 Kaolin 50 Calcium carbonate 20 Greaseless black 20 Soap 2 Vegetable adhesive 5 all thoroughly mixed into a homogeneous mass, molded and dried.

3. A crayon composed of the following ingredients in the following proportions:

all thoroughly mixed into a homogeneous mass, molded and dried.

4. A crayon composed of the following ingredients in the following proportions:

Parts Charcoal 150 Kaolin 50 Calcium carbonate 20 Non-acid soap 2 Vegetable adhesive 5 all thoroughly mixed into a homogeneous mass, molded and dried.

CHARLES E. DANIEL. 

